Anaesthetics
Key points
Unfasted/vomiting patients present an aspiration risk when undergoing general anaesthetic
Rapid sequence induction using IV agents such as Etomidate and Succinylcholine is often necessary
Endotracheal tube sizes
Internal diameter is (age/4) +4 for uncuffed ETTs, with cuffed tubes being one-half size smaller
Need at least 3.5mm tube for flexible bronchoscope
Positive end expiratory pressure - PEEP keeps lungs/alveoli distended
Higher PEEP can correct V/Q mismatch
Increased PIP - Secretions, decreased lung compliance
Ventilator settings
Assist control ventilation (ACV) - Assists all patient spontaneous breaths, will control if breaths drop below a set rate
Others: Synchronised intermittent mandatory ventilation (SIMV), Pressure support (PS), Airway pressure release ventilation (APRV)
High-frequency oscillatory ventilation (HFOV)
Used if mechanical ventilation not successful
Mechanism proposed to be convection - inspiratory gases flowing in centre of airway, expiratory at sides
Anaesthetic considerations in special groups
Neonates
Neonates are prone to post operative apnoea due to immature chemoreceptors and the fact that anaesthetics decrease diaphragm and chest wall muscle tone
Elective surgery on neonates below a certain post conceptual age (cut-offs vary, usually between 50-60 weeks PCA) should include overnight inpatient apnoea monitoring
Trisomy 21
Large tongue
OSA - hypotonia
Narrow trachea
Cardiac abnormalities
Atlanto- axial instability
Thoracoscopy
Arrhythmias, mediastinal shift, hypertension or hypotension, hypercapnia, hypoxemia, re-expansion pulmonary oedema, atelectasis and pneumonia
Congenital heart disease (CHD)
Apart from ACEi and ARBs, most cardiac medications should be continued pre op
Consider and avoid parodoxical air emboli
Intra-op antibiotic prophylaxis to prevent endocarditis should be given for:
Unrepaired CHD
CHD repaired with prosthetics
Cardiac transplant patients
Cyanotic patients
Polycythaemic patients may need bleeding first
May be thrombocytopaenic and have deranged clotting factors
Cardiac index:
Cardiac output L/min/body surface area
Normal is 3.5-4.5 L/min/m2
Inotropes and vasopressors
Adrenaline
Mixed αβ receptor action - positive inotrope and peripheral vasoconstriction
Noradrenaline
Primarily α agonist - peripheral vasoconstriction. Used in septic shock
Dobutamine
β1, weak β2 agonist - positive inotrope - vasodilator
Dopamine - αβδ receptors
Low dose- renal, splanchnic vasodilation
Mid dose- positive inotrope
High dose- peripheral vasoconstriction
Milrinone - phosphodiesterase inhibitor
Increases intracellular cyclic AMP
Positive inotrope and vasodilator
Blood gases
pH decreases (more acidotic) when temperature increases
pO2, pCO2 increase when temperature increases
Anion gap
([Na+] +[K+]) – ([Cl-] + [HCO3-])
Used to interpret acid-base imbalance disorders e.g., is it a disorder that is producing excess anions
Examples of disorders with increased anion gap:
Lactic acidosis
Diabetic ketoacidosis
Examples of disorders with normal anion gap:
Uro-enteric fistula/Ureterosigmoidostomy
Adrenal insufficiency
Pancreatic fistula
Page edited by Mrs Charnjit Seehra BSc November 2024
References
Holcomb and Ashcraft’s Pediatric Surgery, 7th edition, 2020, Chapter 3
Advanced Life Support Group, APLS
Mora Carpio AL, Mora JI. Ventilator Management. [Updated 2023 Mar 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing
Meyers M, Rodrigues N, Ari A. High-frequency oscillatory ventilation: A narrative review. Can J Respir Ther. 2019;55:40-46. Published 2019 May 2. doi:10.29390/cjrt-2019-004
VanValkinburgh D, Kerndt CC, Hashmi MF. Inotropes and Vasopressors. [Updated 2023 Feb 19]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing
Pandey DG, Sharma S. Biochemistry, Anion Gap. [Updated 2023 Jul 10]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing